Dark Matter Could Form Stars, New Theory Says

85% of matter in the universe is dark matter, astrophysicists say. Which might make you  wonder what all this stuff is doing. I mean, some of the matter in the universe has learned to  walk and talk, so why is dark matter so boring. In case you’ve been wondering too,  astrophysicists now say that some of this dark matter might form stars, sort of,  which can explode, sort of. Let’s have a look. Dark matter is one of the explanations that  astrophysicists have come up with to explain numerous ano

malous observations they have  been making during the past century. It basically seems like the pull of gravity  is stronger than it should be though this becomes noticeably only on large scales.  Galaxies rotate faster than they should, galaxies in clusters move too fast,  gravitational lenses are too strong. The hypothesis of dark matter has it that  this happens because there is more stuff in galaxies and galaxy clusters, it’s just that  we can’t see it. The alternative explanation is that th

e law of gravity doesn’t work as  we think it does. Of these two hypotheses, dark matter is currently the more popular one. We know very little about dark matter, if that  exists, which it may not. That’s because to explain observations, dark matter just needs  to be dark and matter and not clump too much. Featureless stuff fits the bill just fine. However, particle physicists like the idea that it’s some kind of particle and they have come  up with all kinds of ideas for just what that particle

could be. There are WIMPS and MACHOs and  Macros and all kinds of supersymmetric particles and massive gravitons and what not. Though  there’s no evidence any of those actually exist. The new paper is about one of those particles  called an axion-like particle. Axions were first proposed in the late 1970 to make the standard  model of particle physics somewhat prettier. Yes, they are named after a washing  detergent because they were supposed to, you know, wash away what particle physicists  co

nsidered to be a blemish in the laws of nature, that’s a constant whose value they don’t  like because they think it’s too small. Unfortunately, if axions existed, they would  be emitted in large numbers from neutron stars, and the neutron stars would  cool very quickly. By 1980 it was clear that observations were just  incompatible with the existence of axions. After that happened, physicists came up  with various amendments to the original axion hypothesis that would make the  particle more di

fficult to detect. So not only was the axion invented for an  unscientific reason – it was to make a perfectly fine theory prettier.  But after it had been ruled out, particle physicists made it even more unscientific  by amending a theory that didn’t explain anything. These new types of axions have now grown to  an entire army called “axion-like particles” and there are dozens of experiments looking for  those particles. They continue to not find them. But about the paper. If dark matter exists

  and if it’s made of these axions and if these axions have the right masses and right  interactions, then they can condense to form compact objects called solitons. This is because  axions are a type of particle called boson, and bosons can undergo Bose-Einstein  condensation. Yes, it’s Albert again. These means that given the right circumstances,  axions just lump onto each other. They clump, basically. The idea has been around for  about 10 years and those axion clumps have been called “axion

stars”.  They don’t look anything like our stars though because they don’t do nuclear  fusion. There are no nuclei to fuse there. Further calculations then showed that if the  axion starts get too big they become unstable, and if they become unstable, they could  explode. And if they could explode that could release radiation which would heat up the  gas in the vicinity. And that might be observable. And this is what they looked at in the new  paper. They asked: If those axion stars were produc

ed in the early universe, and they exploded, what would this have done to the gas because that could still be observable today. They looked  at CMB data and didn’t find any evidence of axion star explosions. As it’s common habit among  physicists, this isn’t called a negative result, but an “interesting constraints”. And also  in line with physicists’ habits, they then say that a next generation of experiments  might be able to find the missing evidence. This next generation of experiments are v

arious  planned radio telescopes that will be looking for old hydrogen emissions which might come  from the gas that might have been affected by the axion stars. This type of experiment  has become known as 21-centimeter astronomy because this hydrogen emission line is  today approximately of the wavelength of 21 centimeters. 21-centimeter astronomy is  basically the next big thing in astronomy and that’s why the current game of theorists is  to make “predictions” for those experiments. Ok, let’

s sum it up. If dark matter exists, which  it may not, and if it’s made of axions, for which there is no reason, and if these axions form stars  , and if these stars have the right properties to explode, and if the axions couple strongly enough  to releases photons, then that could leave some observable traces in the interstellar gas, that  could probably also be caused by many other astrophysical effects. The most interesting  part is that people still get paid for this. Did you know, I have a

Quantum Mechanics course on  Brilliant.org. Its a beginners course that you can take without any background knowledge. It'll  introduce you to topics such as interference, super positions and entanglement, the uncertainty  principle, and Bell's theorem. And afterwards, you can continuing learning more about your favorite  topics in science, computer science, or maths. All courses on Brilliant come with interactive  visualizations and follow up questions. It's really an easy and fun way to learn

something new.  If you want to try it out for free, use our link: brilliant.org/sabine. First 30 days are free and  the first 200 of you to use this link will get 20% off the annual premium subscription.  Thanks for watching, see you tomorrow.